Client/server computing has become more and more important over the past few years in the information technology world. This type of distributed computing allows one machine to delegate some of its work to another machine that might be, for example, better suited to perform that work. For example, the server could be a high-powered computer running a database program managing the storage of a vast amount of data, while the client is simply a desktop personal computer (PC) which requests information from the database to use in one of its local programs.
Message queuing (also known as message brokering) data processing technology has become more and more prevalent in today's client/server computer networks. This technology permits a client computer system to communicate with a server computer system even though these two systems are very different to each other, in terms of operating system, data format and communication protocol. Further, due to the asynchronous nature of this technology, the client can send the server a message and the server can store the message in a queue and process and respond to the message at a later time. This is quite different from the synchronous client/server models which have required the client and server to converse in real time (e.g., the client waits for the server to respond before the client carries on with other tasks).
Message queuing and commercially available message queuing products are described in "Messaging and Queuing Using the MQI", B. Blakeley, H. Harris & R. Lewis, McGraw-Hill, 1994, and in the following publications which are available from IBM Corporation: "An Introduction to Messaging and Queuing" (IBM Document number GC33-0805-00) and "MQSeries--Message Queue Interface Technical Reference" (IBM Document number SC33-0850-01). IBM and MQSeries are trademarks of IBM Corporation. IBM's MQSeries messaging software products provide transactional messaging support, synchronising messages within logical units of work in accordance with a messaging protocol which gives assured once and once-only message delivery even in the event of system or communications failures. MQSeries products provide assured delivery by not finally deleting a message from storage on a sender system until it is confirmed as safely stored by a receiver system, and by use of sophisticated recovery facilities. Prior to commitment of transfer of the message upon confirmation of successful storage, both the deletion of the message from storage at the sender system and insertion into storage at the receiver system are kept `in doubt` and can be backed out atomically in the event of a failure. This message transmission protocol and the associated transactional concepts and recovery facilities are described in international patent application WO 95/10805 and U.S. Pat. No. 5,465,328, which are incorporated herein by reference.
In an asynchronous client/server network, such as one that uses a message and queuing software architecture, it is becoming more and more common to provide a group of servers in which each server of the group is capable of satisfying a client's request. This way, a client's request can be served more quickly because if one server is busy the request can be forwarded on to another server. Typically, a workload management unit on the client side makes a decision as to which server should be assigned to handle a particular request, using availability data from each server as a basis for making the decision. If all of such availability data is not yet available, the workload management unit waits until it receives such data and then uses the complete set of data to make a decision on a server. The client request, with an appended indication of the server selected by the workload management unit, is then placed in a transmission queue where it awaits transmission to the selected server. The client also writes some information about the queued request, including the indication of the selected server, to local storage so that the request can be sent again from the client to the server if a transmission problem occurs such that the server has not received the transmitted client request.
The present state of the art in this area is disadvantageous because the workload management unit must involve complex software portions which must continually check the state of the server availability data for each server to determine when all of such data has been completed received from the servers. This complex software programming adds a great deal of extra cost to the overall system.
Further, if all of the server availability data has not yet been received, a request cannot be transmitted to the server group, thus holding up the data transmission process at the client side. This is highly disadvantageous, especially in an environment where a fast transmission speed is very important.